The present invention is directed to a method of optimizing the performance of a multi-unit power plant and more specifically for the integrated control of the power boiler and steam distribution (including turbine generator) system in the pulp and paper industry.
In the pulp and paper industry and for that matter in any petro-chemical industry in-house multi-unit power plants are used both to generate electrical energy and steam which is used as part of the processing operation; for example, in a paper mill in the paper industry. The steam energy is a significant fraction of the total energy produced by the power plant. Moreover, this steam energy is used for purposes independent of generation of electrical power.
This is in contrast to a typical power industry system where all steam from the turbine generator is returned via condensate to the power boiler for reheating along with make-up water. In the paper industry, for example, a significant portion of steam is extracted from the turbine generator at pressures of, for example, 600, 160 and 60 pounds per square inch and used to provide steam energy to many different types of production units, for example, paper machines, dryers, evaporators, in the pulp and paper manufacturing process.
Thus, it is apparent that the control criteria for energy optimization in the typical power industry systems are inadequate in the paper industry. Yet another difference especially in the paper industry is the use of wood chips as one of the fuels for the power boiler in addition to both coal and oil. Wood chips because of the change in their moisture and type of wood will vary in their effective heating value. In addition, this heating value may be lessened because of the tendency of the wood chips to form soot in the power boiler to again lower efficiency. Moreover, the perturbations in fuel characteristics and their resulting effect on efficiency cannot be directly and accurately measured. This is especially true in present day electrical power industry control systems.
There are several specific disadvantages in the case of pulp mills with present energy management systems. For example, in power boilers which are fired with two fuels, for example, coal or wood chips as a base load fuel and oil as the swing fuel, the base load fuel is not adjusted for changes in operating conditions. The loading of individual power boilers is based solely on steam production requirements not on operating efficiency. The efficiencies of the various steam turbines are not taken into account when loadings are distributed to the steam engine. Finally, presently available systems are not able to compensate quickly for changes in electrical and steam demands. The result is higher rate charges from the local electrical utility due to exceeding the peak demand level.